This invention relates to a method for distributing electric power in telecommunication central office equipment intended to operate at voltages within a determined range.
As the equipment operates continuously correctly only when the input voltage is situated within a limited range around a nominal voltage, the power is distributed in such way that the voltage is situated within a determined range.
For the power distribution of a telephone network, the reference voltage is for instance 48 V and said range from 38 V to 56 V.
Telecommunication standards, for example ETSI (European Telecommunications Standard Institute) and BELCORE standards, require that the equipment should keep operating normally when the input voltage, for example the DC voltage from a battery or a rectifier, drops temporarily below the lower limit of this range.
Such voltage drop can take place when the power is switched, for instance by means of relays, from one power supply to another. The duration of such input voltage drop can vary between 0 and 30 ms.
In order to avoid that the distribution is cut off during a short voltage drop, capacitors are used which keep the voltage constant, and thus above the lowest voltage of said voltage range, during the input voltage drop.
These big capacitors are costly and voluminous. The distribution racks used for distributing are consequently relatively big and expensive. Extra sub-racks may be required for the big capacitors.
The aim of the invention is to obviate this drawback and to offer a method for power distribution, avoiding the use of big capacitors and permitting to use a relatively economic and compact equipment for the distribution.
In accordance with the invention, this object is accomplished in a method for distributing power according to which the voltage of the distributed power is allowed to drop below the lowest voltage of the range, but only temporarily.
This is completely against the general idea that the voltage may never drop below the lower limit of the prescribed range.
Unexpectedly, it was found that such voltage drop is permissible during a short time and for instance for the duration of the above mentioned input voltage drop which the prior art methods compensate with capacitors.
Preferably, according to the invention, the voltage of the distributed power is allowed to drop below this lowest voltage during the complete duration of said input voltage drop, this is thus in practice during 0 ms to 30 ms.
The invention also relates to a device for distributing electric power in telecommunication central office equipment intended to operate at voltages within a determined range, particularly suited for the application of the above described method of the invention.
The device is characterised in that it comprises means for allowing the voltage of the distributed power to drop temporarily below the lowest voltage of the range.